The present invention relates to a silver halide photographic material, in particular, a super-high contrast negative photographic material suitable for a silver halide photographic material for use in photomechanical process.
In photomechanical process of the field of graphic arts, a continuous tone photographic image is converted to a so-called halftone dot image expressing the nuances of light and dark of the image by the sizes of dot areas and combined with a photographed image of characters and line images, to thereby make a printing plate precursor. A silver halide photographic material for use for such a purpose is required to have super-high contrast photographic characteristics of distinct discriminability of an image area and a non-image area to well reproduce the characters, line images and halftone dot image.
As the system to respond to the desire for super-high contrast photographic characteristics, a so-called lith developing system is known, which comprises the step of processing a silver halide photographic material comprising a silver chlorobromide with a hydroquinone developing solution of an extremely low effective concentration of a sulfite ion, to thereby form a high contrast image. However, since the sulfite ion concentration in the developing solution is low according to this method, the developing solution is exceedingly unstable to air oxidation and a great amount of a replenisher must be replenished for maintaining liquid activity stable.
As the image-forming systems solving the problem of instability of image formation by the lith developing system, and capable of obtaining super-high contrast photographic characteristics by processing a photographic material with a developing solution having a good storage stability, for example, U.S. Pat. Nos. 4,166,742, 4,168,977, 4,221,857, 4,224,401, 4,243,739, 4,269,922, 4,272,606, 4,311,781, 4,332,878, 4,618,574, 4,634,661, 4,681,836 and 5,650,746 are exemplified. These are systems of processing a surface latent image type silver halide photographic material containing a hydrazine derivative with a developing solution containing hydroquinone/metol or hydroquinone/phenidone as a developing agent containing 0.15 mol/liter or more of a sulfurous acid preservative and having pH of from 11.0 to 12.3 to thereby form a super-high contrast negative image having a xcex3 value of more than 10. According to these systems, super-high contrast and high sensitive photographic characteristics can be obtained and a sulfite of high concentration can be added to a developing solution, accordingly the stability to air oxidation of the developing solution is extraordinarily improved as compared with conventional lith developing solutions.
For sufficiently exhibiting a super-high contrast image due to a hydrazine derivative, it has been necessary to perform processing with a developing solution having a pH value of 11.5 or higher. Although a sulfurous acid preservative of high concentration has made it possible to heighten the stability of a developing solution, it is necessary to use a developing solution having a high pH value as described above to obtain a super-high contrast photographic image. A developing solution is liable to be air-oxidized and unstable even when a preservative is used, therefore various means have been contrived to realize a super-high contrast image with a lower pH value aiming at further improvement of stability.
For example, methods of using highly active hydrazine derivatives and nucleating accelerators for obtaining a super-high contrast image with a developing solution having pH of lower than 11.0 are disclosed in U.S. Pat. No. 4,269,929 (corresponding to JP-A-61-267759 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d)), U.S. Pat. No. 4,737,452 (corresponding to JP-A-60-179734), U.S. Pat. Nos. 5,104,769, 4,798,780, JP-A-1-179939, JP-A-1-179940, U.S. Pat. Nos. 4,998,604, 4,994,365 and JP-A-8-272023.
Also, a high contrast material containing a dimeric hydrazine derivative is disclosed in U.S. Pat. No. 6,228,566.
Since silver halide photographic materials for use in such an image-forming system contain highly active compounds, they are accompanied by various problems, such as the problems of storage stability, e.g., sensitivity fluctuates and fog increases during storage, and the aging stability of a coating solution at production is poor and the sensitivity fluctuation of the photographic material produced is large. Many of the causes are attributable to the fact that the sensitivity of emulsions is high, therefore further techniques of high sensitization have been desired.
An object of the present invention is to provide a high contrast and high sensitive silver halide photographic material.
The above object of the present invention has been achieved by the following means.
(1) A silver halide photographic material comprising a support having provided thereon at least a silver halide emulsion layer, which contains at least one compound represented by the following formula (I), and has a characteristic curve of gamma value being 5.0 or more in optical density of from 0.3 to 3.0 on the characteristic curve shown on the orthogonal axis of coordinates having equal unit length expressed by logarithmic exposure amount (x axis) and optical density (y axis):
(X)lxe2x80x94(L)mxe2x80x94(Axe2x80x94B)nxe2x80x83xe2x80x83(I)
wherein X represents a silver halide-adsorptive group having at least one of N, S, P, Se and Te atom, or a light absorptive group; L represents a divalent linking group having at least one of C, N, S and O atom; A represents an electron donative group; B represents a releasing group or a hydrogen atom, which forms radical A. by releasing or deproton after oxidation; l and m each represents an integer of from 0 to 3; and n represents 1 or 2.
The gamma value is preferably from 5.0 to 100, particularly preferably from 5.0 to 30.
(2) The silver halide photographic material as described in the above item (1) which contains a hydrazine compound.
(3) The silver halide photographic material as described in the above item (1) or (2), wherein the pH of the film surface of the emulsion layer side is 6.0 or less.
The film surface pH is preferably from 4.5 to 6.0, because when the film surface pH is less than 4.5, the progress of film hardening of the emulsion layer is liable to be delayed.
(4) The silver halide photographic material as described in the above item (1), (2) or (3), wherein the hydrazine compound is a dimer comprising monomers containing both an acylhydrazide moiety and a nicotinamide moiety linked by a linking group.
(5) The silver halide photographic material as described in the above item (4), wherein the dimer comprising monomers containing both an acylhydrazide moiety and a nicotinamide moiety linked by a linking group is represented by the following formula (1) or (2): 
wherein each monomer linked by linking group L may be the same or different; J represents a nicotinamide residue; E represents a substituted aryl group or a heterocyclic ring; one of A1 and A2 represents a hydrogen atom and the other represents a hydrogen atom, an acyl group or an alkyl- or aryl-sulfonyl group, any of which may be substituted; D represents a blocking group; L represents a divalent linking group; and Xxe2x88x92 represents an anionic counter ion.